Electronic 'crowd behavior' revealed in semiconductors

Jul 07, 2007
Electronic 'crowd behavior' revealed in semiconductors
Physicists at JILA have confirmed subtle "collective behavior" among electronic structures in semiconductors, research that may help improve the design of optoelectronic devices. In the first image (#1, showing new experimental data), matching large peaks in the foreground, showing energy intensity ranging from low in blue to high in red, indicate that pairs of large electronic particles called excitons are oscillating in concert as they absorb ultrafast laser light and emit energy at various frequencies. The data match new theoretical models accounting for all electronic properties of semiconductors (image #2) much better than older theoretical models. Credit: JILA and University of Marburg

Like crowds of people, microscopic particles can act in concert under the right conditions. By exposing crowd behavior at the atomic scale, scientists discover new states and properties of matter.

Now, ultrafast lasers have revealed a previously unseen type of collective electronic behavior in semiconductors, which may help in the design of optoelectronic devices. The work at JILA, a joint venture of the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder, is described in a new paper in the Proceedings of the National Academy of Sciences.

Electronic 'crowd behavior' revealed in semiconductors
Physicists at JILA have confirmed subtle "collective behavior" among electronic structures in semiconductors, research that may help improve the design of optoelectronic devices. Credit: JILA and University of Marburg

Design of optoelectronic devices, like the semiconductor diode lasers used in telecommunications, currently involves a lot of trial and error. A designer trying to use basic theory to calculate the characteristics of a new diode laser will be off by a significant amount because of subtle interactions in the semiconductor that could not be detected until recently.

To shed light on these interactions, the JILA team used a highly sensitive and increasingly popular method of manipulating laser light energy and phase (the point in time when a single light wave begins) to reveal the collective behavior of electronic particles that shift the phase of any deflected light. Their work is an adaptation of a technique that was developed years ago by other researchers to probe correlations between spinning nuclei as an indicator of molecular structure (and led to a Nobel prize).

In the latest JILA experiments, a sample made of thin layers of gallium arsenide was hit with a continuous series of three near-infrared laser pulses lasting just 100 femtoseconds each. Trillions of electronic structures called excitons were formed. Excitons are large, fluffy particles consisting of excited electrons and the “holes” they left behind as they jumped to higher-energy vibration patterns.

By tinkering with the laser tuning—the frequency and orientation of the electric field—and analyzing how the semiconductor altered the intensity and phase of the light, the researchers identified a subtle coupling between pairs of excitons with different energy levels, or electron masses. The experimental data matched advanced theoretical calculations of the electronic properties of semiconductors, confirming the importance of the collective exciton behavior—and dramatically demonstrated the superiority of those calculations over simpler models of semiconductor behavior (see graphic).

Citation: T. Zhang, I. Kuznetsova, T. Meier, X. Li, R.P. Mirin, P. Thomas and S.T. Cundiff. Polarization-dependent optical two-dimensional Fourier transform spectroscopy of semiconductors. Proceedings of the National Academy of Sciences. Scheduled to be posted on-line July 6.

Source: National Institute of Standards and Technology

Explore further: Breakthrough in OLED technology

add to favorites email to friend print save as pdf

Related Stories

Semiconductor works better when hitched to graphene

Feb 20, 2015

Graphene – a one-atom-thick sheet of carbon with highly desirable electrical properties, flexibility and strength – shows great promise for future electronics, advanced solar cells, protective coatings ...

Chassis 1A part from early computer resurfaces

Feb 05, 2015

The National Museum of Computing has reported the discovery of a rare part of an early computer. With reconstruction expected to be completed later this year, the reconstruction team is eager to find out ...

Skin device uses motion to power electronics

Jan 29, 2015

Can a skin patch power wearables? Skin-based generators have become an area of focus among researchers working on how to scavenge muscle motion whereby skin becomes a charge-collector. A detailed report in ...

Building a more versatile frequency comb

Feb 17, 2015

Frequency combs are the rulers of light. By counting a wavelength's many oscillations, they measure distance and time with extraordinary precision and speed.

Recommended for you

Breakthrough in OLED technology

11 hours ago

Organic light emitting diodes (OLEDs), which are made from carbon-containing materials, have the potential to revolutionize future display technologies, making low-power displays so thin they'll wrap or fold ...

Throwing light on a mysterious human 'superpower'

14 hours ago

Most people, at some point in their lives, have dreamt of being able to fly like Superman or develop superhuman strength like the Hulk. But very few know that we human beings have a "superpower" of our own, ...

New filter could advance terahertz data transmission

Feb 27, 2015

University of Utah engineers have discovered a new approach for designing filters capable of separating different frequencies in the terahertz spectrum, the next generation of communications bandwidth that ...

The super-resolution revolution

Feb 27, 2015

Cambridge scientists are part of a resolution revolution. Building powerful instruments that shatter the physical limits of optical microscopy, they are beginning to watch molecular processes as they happen, ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.